1. Field of the Invention
This invention relates generally to optical telecommunication modules which include one or more photonic integrated circuit (PIC) chips and more particularly to the deployment of one or more of such PIC chips with an off-chip booster optical amplifier to boost the multiplexed channel signal output of the chip or chips.
2. Description of the Related Art
Semiconductor photonic integrated circuit (PIC) chip architecture has recently been developed at Infinera Corporation comprising multiple transmitter or receiver channels, or both, formed on a single semiconductor chip optically coupled with an optical combiner which provides an off-chip output of plural multiplexed channel signals. This architecture includes one or more photonic integrated circuits (PICs) on a single chip, such as an InP chip using, for example, InGaAsP/InP or InAlGaAs/InP alloys. These monolithic chips are called transmitter photonic integrated circuits (TxPICs) or receiver photonic integrated circuits (RxPICs). The TxPIC chips include multiple signal channels of different wavelengths which approximate a standardized wavelength grid, such as the ITU grid, and the number of channels on any one PIC chip may range, for example, from 8 channels to 40 channels. Each chip, therefore, includes a plurality of signal channels or optical channel paths with each path comprising a DFB or DBR laser source followed by and electro-optic (EO) modulator, such as an electro-absorption (EA) modulator or a Mach-Zehnder (M-Z) modulator and, possibly, followed by an optional semiconductor optical amplifier (SOA) and/or photodetector (PD), such as a PIN photodiode or an avalanche photodiode (APD). The modulated optical signals from the multiple channel paths are launched into an optical combiner, having inputs optically coupled with each of the channel paths. The optical combiner is preferably a wavelength-selective optical combiner, such as, an Echelle grating or an array waveguide array (AWG). However, it may also be a power combiner, such as a star coupler or an multi-mode interference (MMI) coupler. An AWG type of optical combiner is preferred because of its low insertion losses. The multiplex channel signals are, then, passed, via an on-chip output waveguide from the optical combiner, to an exit port on the chip where the multiplexed channel output is optically coupled to a fiber transmission link. The output waveguide may also include a mode converter. Further details relating to this type of TxPIC architecture can be found in U.S. patent applications, Ser. No. 10/267,331; Ser. No. 10/267,330; and Ser. No. 10/267,346, all filed on Oct. 8, 2002, which patent applications are incorporated herein by their reference.
In the deployment of multiple TxPIC chips at the optical communication module level, it is necessary to optically combine the outputs from multiple TxPIC chips for launching them on a fiber transmission link. In order to perform this function, it has been proposed that in order to effectively accomplish this function to employ wavelength-selective multiplexing components that comprise a plurality of four-port interleavers and band combining dichroic filters to combine the multiplexed outputs of multiple TxPIC chips. These components, while presently available, are highly expensive and also suffer from high yield issues due to their complexity and newness in development and deployment.